基于磁共振成像系统的头部三维电阻抗成像技术研究
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摘要
在现代医学中,高分辨率的、精确的电阻率分布图对许多疾病的诊断和治疗都起着十分重要的作用。基于磁共振成像系统的生物电阻抗成像技术(MREIT)是近几年发展起来的新型非入侵式成像技术。由于该技术的成像精确度与空间分辨率都比普通阻抗成像技术高很多,受到越来越多的阻抗成像技术工作者的关注。目前MREIT技术存在的问题有:1,大多数MREIT成像算法都是基于二维物体的阻抗成像;2,成像物体在核磁共振成像系统(MRI)中的旋转问题。这两个问题阻碍了MREIT技术的继续发展。本论文针对上述两个影响MREIT技术发展的问题展开研究,首先提出了一种三维MREIT成像算法,实现了对三维物体的阻抗重建,然后针对成像物体在MRI系统中的旋转问题,提出了两个仅利用单个磁感应强度测量值对三维物体电导率分布进行重建的MREIT算法。上述算法的可行性与有效性均在头模型上进行了计算机仿真实验验证,并取得了令人满意的结果。本论文安排如下:
1,第一章简述了选题意义。首先概述了生物电阻抗分布图的医学研究意义、传统生物电阻抗成像技术对头部进行阻抗成像的难点,然后介绍了基于磁共振成像系统的生物电阻抗成像技术的发展及研究潜力,最后介绍了本论文的主要研究内容与主要创新点。
2,第二章详细介绍了基于磁共振成像系统的生物电阻抗成像技术的背景知识。首先对磁共振成像的成像原理做了简单的介绍,然后介绍了利用磁共振成像系统检测物体内电流密度分布的电流密度成像技术的成像过程与成像原理,最后论述了基于磁共振成像系统的生物电阻抗成像技术的发展历程、正问题、逆问题与目前面临的难点问题。
3,第三章针对目前MREIT技术大多是对二维物体进行阻抗成像的问题,将二维MREIT算法进行了三维扩展,从正问题、逆问题、解的唯一性等方面对此三维MREIT算法进行了详细论述。然后利用此三维MREIT算法在四层球头模型上进行两组仿真实验,分别利用此算法检测头部真实电导率分布及检测由脑出血与脑缺血引起的大脑电导率的变化。两组仿真实验结果均取得了令人满意的结果。
4,第四章针对目前阻碍MREIT发展的最大问题,成像物体在MRI系统中的旋转问题,原创性地提出了一种基于径向基函数的MREIT算法,RBF-MREIT算法。该算法仅利用单个磁感应强度测量值对三维物体电导率分布进行重建,有效地解决了成像物体在MRI系统中的旋转问题。在三层球头模型与真实头模型上进行的仿真实验证明了该算法的可行性与有效性。
5,第五章提出了一种新颖的、基于表面响应模型的MREIT算法,RSM-MREIT算法。该算法利用表面响应模型方法与单纯形法构建函数输入—输出关系式并对最优电导
Accurate electrical impedance image is important in medical applications. Magnetic Resonance Electrical Impedance Tomography (MREIT) is a new, noninvasive conductivity imaging modality that integrates current density imaging (CDI) and traditional electrical impedance tomography (EIT). Both the accuracy and spatial resolution of MREIT are better than traditional EIT, and more and more scientists pay attention to the research of it. The two problems that limit the development of MREIT are: 1) Current MREIT algorithms reconstruct only two-dimensional (2D) subject conductivity distribution. 2) The rotation problem exists in magnetic resonance imaging (MRI) system. Aiming at these two problems, this thesis makes systematical research of MREIT. A 3D MREIT algorithm is firstly proposed. Then two original MREIT algorithms that reconstruct subject conductivity image without rotation are proposed and satisfactory simulation results are obtained. This thesis is organized as follows:In chapter 1, the research meaning is briefly introduced. Firstly, the medical application of electrical impedance image and the difficulty of traditional EIT were introduced briefly. Then the development and the research potential of MREIT were stated in detail. Finaly, the strcture of the thesis and the main purpose of the research were presented.In Charpter 2, the imaging theory of magnetic resonance imaging (MRI) system and current density imaging (CDI) technique were introduced, and then the development history of the forward problem, inverse problem and the difficulty of MREIT were stated.In charpt 3, a 3D MREIT algorithm was proposed and the forward problem, inverse problem and the uniqueness of the solution were discussed in detail. Computer simulations were conducted on a four-sphere head model to detect the availability of the proposed 3D MREIT algorithm and encouraging simulation results were obrained.In charpt 4, a novel MREIT algorithm, RBF-MREIT algorithm, was proposed. This new algorithm reconstrucs 3D subject conductivity using only one component magnetic flux density measurement, and therefore solves the rotation problem in MREIT effectively. A series of computer simulations were conducted on a three-sphere head model and a realistic-geometry head model, and the simulation results are encouraging.In charpt 5, another MREIT algorithm, RSM-MREIT algorithm was proposed to reconstruct 3D subject conductivity image without roation. Computer simulations were conducted on a three-sphere head model and a realistic-geometry head model. The promising simulation results demonstrated the feasibility of the proposed RSM-MREIT algorithm.Charpt 6 is the conclusion and suggestions for fouture research. The research content and original point of the present research was concluded. Accorting to the defects of the presented research, future research directions were stated.
1,第一章简述了选题意义。首先概述了生物电阻抗分布图的医学研究意义、传统生物电阻抗成像技术对头部进行阻抗成像的难点,然后介绍了基于磁共振成像系统的生物电阻抗成像技术的发展及研究潜力,最后介绍了本论文的主要研究内容与主要创新点。
2,第二章详细介绍了基于磁共振成像系统的生物电阻抗成像技术的背景知识。首先对磁共振成像的成像原理做了简单的介绍,然后介绍了利用磁共振成像系统检测物体内电流密度分布的电流密度成像技术的成像过程与成像原理,最后论述了基于磁共振成像系统的生物电阻抗成像技术的发展历程、正问题、逆问题与目前面临的难点问题。
3,第三章针对目前MREIT技术大多是对二维物体进行阻抗成像的问题,将二维MREIT算法进行了三维扩展,从正问题、逆问题、解的唯一性等方面对此三维MREIT算法进行了详细论述。然后利用此三维MREIT算法在四层球头模型上进行两组仿真实验,分别利用此算法检测头部真实电导率分布及检测由脑出血与脑缺血引起的大脑电导率的变化。两组仿真实验结果均取得了令人满意的结果。
4,第四章针对目前阻碍MREIT发展的最大问题,成像物体在MRI系统中的旋转问题,原创性地提出了一种基于径向基函数的MREIT算法,RBF-MREIT算法。该算法仅利用单个磁感应强度测量值对三维物体电导率分布进行重建,有效地解决了成像物体在MRI系统中的旋转问题。在三层球头模型与真实头模型上进行的仿真实验证明了该算法的可行性与有效性。
5,第五章提出了一种新颖的、基于表面响应模型的MREIT算法,RSM-MREIT算法。该算法利用表面响应模型方法与单纯形法构建函数输入—输出关系式并对最优电导
Accurate electrical impedance image is important in medical applications. Magnetic Resonance Electrical Impedance Tomography (MREIT) is a new, noninvasive conductivity imaging modality that integrates current density imaging (CDI) and traditional electrical impedance tomography (EIT). Both the accuracy and spatial resolution of MREIT are better than traditional EIT, and more and more scientists pay attention to the research of it. The two problems that limit the development of MREIT are: 1) Current MREIT algorithms reconstruct only two-dimensional (2D) subject conductivity distribution. 2) The rotation problem exists in magnetic resonance imaging (MRI) system. Aiming at these two problems, this thesis makes systematical research of MREIT. A 3D MREIT algorithm is firstly proposed. Then two original MREIT algorithms that reconstruct subject conductivity image without rotation are proposed and satisfactory simulation results are obtained. This thesis is organized as follows:In chapter 1, the research meaning is briefly introduced. Firstly, the medical application of electrical impedance image and the difficulty of traditional EIT were introduced briefly. Then the development and the research potential of MREIT were stated in detail. Finaly, the strcture of the thesis and the main purpose of the research were presented.In Charpter 2, the imaging theory of magnetic resonance imaging (MRI) system and current density imaging (CDI) technique were introduced, and then the development history of the forward problem, inverse problem and the difficulty of MREIT were stated.In charpt 3, a 3D MREIT algorithm was proposed and the forward problem, inverse problem and the uniqueness of the solution were discussed in detail. Computer simulations were conducted on a four-sphere head model to detect the availability of the proposed 3D MREIT algorithm and encouraging simulation results were obrained.In charpt 4, a novel MREIT algorithm, RBF-MREIT algorithm, was proposed. This new algorithm reconstrucs 3D subject conductivity using only one component magnetic flux density measurement, and therefore solves the rotation problem in MREIT effectively. A series of computer simulations were conducted on a three-sphere head model and a realistic-geometry head model, and the simulation results are encouraging.In charpt 5, another MREIT algorithm, RSM-MREIT algorithm was proposed to reconstruct 3D subject conductivity image without roation. Computer simulations were conducted on a three-sphere head model and a realistic-geometry head model. The promising simulation results demonstrated the feasibility of the proposed RSM-MREIT algorithm.Charpt 6 is the conclusion and suggestions for fouture research. The research content and original point of the present research was concluded. Accorting to the defects of the presented research, future research directions were stated.
引文
[1] 王妍,任超世,3D—EIT图像重建的研究进展,国外医学生物医学工程分册,26(6):265-268,2003.
[2] 南国芳,王化祥,王超,基于BP神经网络和遗传算法的电阻抗图像重建算法,计量学报,24(4):337-340,2003.
[3] 林磊,莫玉龙,候卫东,电阻抗成像系统的设计和实现,计算机工程,28(7):75-77,2002.
[4] 史学涛,董秀珍,秦明新等,由于电阻抗多频及参数成像数据采集系统的正交序列解调法,第四军医大学学报,21(7):164-166,2000.
[5] 宫莲,黄平,刘茵,一种有效的电阻抗成像的图像重建算法,中国生物医学工程学报,10(3):149-159,1991.
[6] 宫莲,张克潜,用三维各向异性电阻抗成像作人脑活动的研究,清华大学学报(自然科学版),39(5):1-4,1999.
[7] Dong G, Liu H, Bayford RH, Yerworth R, Gao S, Holder D, Yan W, The spatial resolution improvement of EIT images by GVSPM-FOCUSS algorithm, Physiol Meas,25:209-225, 2004.
[8] Sanlnicr GJ, Blue RS, Newell JC, Isaacson D, Electrical Impedance Tomography, IEEE Signal Processing Magazine, 31-43, Nov, 2001.
[9] Davalos RV, Otten DM, Mir LM, Rubinsky B, Electrical Impedance Tomography for Imaging Tissue Electroporation, IEEE Transactions on Biomedical Engineering, 51(5), 761-767, 2004
[10] Holder D, Electrical Impedance Tomography of Brain Function: Its Potencial Advantages for Imaging Epileptic Active. IEE. 1997.
[11] 王保文等.磁场在生物医学中的应用.北京:国防工业出版社.,1990.8
[12] Pething R, Dielectric Properties of Body Tissues, Clinical Phys Physiology Meas, 1987.
[13] Sohwan HP, Analysis of Dielectric Data: Experimence with Biological Materials, IEEE Trans on Electrical Insulation, 20(6):913-921, 1985.
[14] Grant J P et al., Complex Permittivity Differences Between normal and Pathological Tissues: Mechanisms and Medical Significance, Journal of Bioelectricity, 4(2):419-485, 1985.
[15] Lee E Bacher,阻抗技术原理,国外医学生物医学工程分册,12(5),1989.
[16] Boone K, Barber D, Review: Imaging with electricity: Report of the European Conerted Action on Impedance Tomography, Journal of Medical Engineering & Technology, 21 (6):201-232, 1997.
[17] Boone KG, Lewis AM and Holder DS, Imaging the Cortical Spreading Depression by EIT: Implications for Localization of Epileptic Foci, Physiol. Meas, 15(Suppl. 3A):189-198, 1994.
[18] Holder DS, Rao A and Hanquan Y, Imaging of Physiological Evoked Responses by Electrical Impedance Tomography with Cortical Electrodes in the Anaesthetized Rabbit, Physiol Meas, 17(Suppl. 4A): 179-186, 1996.
[19] Barber DC and Seagar AD, Fast reconstruction of resistance images, Clin. Phys. Physiol. Meas., 10: 368-370, 1987.
[20] Metheral P, Barber DC, Smallwood RH, Brown BH, Three dimensional electrical impedance tomography, Nature, 380:509-512, 1996.
[21] Joy M, Scott G, and Henkelman M, In vivo detection of applied electric currents by magnetic resonance imaging, Magnetic Resonance Imaging, 7:1: 89-94, 1989.
[22] Pesikan P, Joy MLG, Scott GC, Henkelman RM, Two-Dimensional Current Density Imaging, IEEE Transactions on Instrumentation and Measurement, 39(6):1048-1053, 1990.
[23] Scott GC, Joy MLG, Armstrong RL, and Henkelman RM, Measurement of nonuniform current density by magnetic resonance, IEEE Trans. Med. Imag, 10: 362-374, 1991.
[24] ider YZ, Muftuler LT, Measurement of AC Magnetic Field Distribution Using Magnetic Resonance Imaging, IEEE Transactions on Medical Imaging, 16(5):617-622, 1997.
[25] Eyuboglu BM, Reddy R and Leigh JS, Imaging electrical current density using nuclear magnetic resonance, ELEKTRIK, 6: 201-214, 1998.
[26] Zhang N, "Electrical impedance tomography based on current density imaging," MSc Thesis University of Toronto, 1992.
[27] 高诺,朱善安,邹凌.电流密度成像及其在生物电阻抗成像中的应用.国外医学生物医学工程分册,2004,27(5):286-289.
[2] 南国芳,王化祥,王超,基于BP神经网络和遗传算法的电阻抗图像重建算法,计量学报,24(4):337-340,2003.
[3] 林磊,莫玉龙,候卫东,电阻抗成像系统的设计和实现,计算机工程,28(7):75-77,2002.
[4] 史学涛,董秀珍,秦明新等,由于电阻抗多频及参数成像数据采集系统的正交序列解调法,第四军医大学学报,21(7):164-166,2000.
[5] 宫莲,黄平,刘茵,一种有效的电阻抗成像的图像重建算法,中国生物医学工程学报,10(3):149-159,1991.
[6] 宫莲,张克潜,用三维各向异性电阻抗成像作人脑活动的研究,清华大学学报(自然科学版),39(5):1-4,1999.
[7] Dong G, Liu H, Bayford RH, Yerworth R, Gao S, Holder D, Yan W, The spatial resolution improvement of EIT images by GVSPM-FOCUSS algorithm, Physiol Meas,25:209-225, 2004.
[8] Sanlnicr GJ, Blue RS, Newell JC, Isaacson D, Electrical Impedance Tomography, IEEE Signal Processing Magazine, 31-43, Nov, 2001.
[9] Davalos RV, Otten DM, Mir LM, Rubinsky B, Electrical Impedance Tomography for Imaging Tissue Electroporation, IEEE Transactions on Biomedical Engineering, 51(5), 761-767, 2004
[10] Holder D, Electrical Impedance Tomography of Brain Function: Its Potencial Advantages for Imaging Epileptic Active. IEE. 1997.
[11] 王保文等.磁场在生物医学中的应用.北京:国防工业出版社.,1990.8
[12] Pething R, Dielectric Properties of Body Tissues, Clinical Phys Physiology Meas, 1987.
[13] Sohwan HP, Analysis of Dielectric Data: Experimence with Biological Materials, IEEE Trans on Electrical Insulation, 20(6):913-921, 1985.
[14] Grant J P et al., Complex Permittivity Differences Between normal and Pathological Tissues: Mechanisms and Medical Significance, Journal of Bioelectricity, 4(2):419-485, 1985.
[15] Lee E Bacher,阻抗技术原理,国外医学生物医学工程分册,12(5),1989.
[16] Boone K, Barber D, Review: Imaging with electricity: Report of the European Conerted Action on Impedance Tomography, Journal of Medical Engineering & Technology, 21 (6):201-232, 1997.
[17] Boone KG, Lewis AM and Holder DS, Imaging the Cortical Spreading Depression by EIT: Implications for Localization of Epileptic Foci, Physiol. Meas, 15(Suppl. 3A):189-198, 1994.
[18] Holder DS, Rao A and Hanquan Y, Imaging of Physiological Evoked Responses by Electrical Impedance Tomography with Cortical Electrodes in the Anaesthetized Rabbit, Physiol Meas, 17(Suppl. 4A): 179-186, 1996.
[19] Barber DC and Seagar AD, Fast reconstruction of resistance images, Clin. Phys. Physiol. Meas., 10: 368-370, 1987.
[20] Metheral P, Barber DC, Smallwood RH, Brown BH, Three dimensional electrical impedance tomography, Nature, 380:509-512, 1996.
[21] Joy M, Scott G, and Henkelman M, In vivo detection of applied electric currents by magnetic resonance imaging, Magnetic Resonance Imaging, 7:1: 89-94, 1989.
[22] Pesikan P, Joy MLG, Scott GC, Henkelman RM, Two-Dimensional Current Density Imaging, IEEE Transactions on Instrumentation and Measurement, 39(6):1048-1053, 1990.
[23] Scott GC, Joy MLG, Armstrong RL, and Henkelman RM, Measurement of nonuniform current density by magnetic resonance, IEEE Trans. Med. Imag, 10: 362-374, 1991.
[24] ider YZ, Muftuler LT, Measurement of AC Magnetic Field Distribution Using Magnetic Resonance Imaging, IEEE Transactions on Medical Imaging, 16(5):617-622, 1997.
[25] Eyuboglu BM, Reddy R and Leigh JS, Imaging electrical current density using nuclear magnetic resonance, ELEKTRIK, 6: 201-214, 1998.
[26] Zhang N, "Electrical impedance tomography based on current density imaging," MSc Thesis University of Toronto, 1992.
[27] 高诺,朱善安,邹凌.电流密度成像及其在生物电阻抗成像中的应用.国外医学生物医学工程分册,2004,27(5):286-289.